The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Automatic shifting power transmissions include a hydraulic system, which supplies power to operate the various clutches and brakes and other elements within the transmission. The hydraulic pressure is limited or controlled in value to provide the most efficient operation that can be obtained.
In more recent transmissions, the hydraulic controls have been advanced to electro-hydraulic controls wherein electrical or electronic signals are available to assist in transmission controls. The electro-hydraulic controls generally comprise a solenoid valve, which receives various signals from a transmission control module (TCM) to supply a pressure signal to the various operating valves of the transmission.
An automatic transmission closed loop control system relies on pressure sensors to perform the closed loop portion of the control. These sensors can be comprised of a multitude of technologies and constructions, but all provide a signal indicative of fluid pressure of the circuit being measured. (See U.S. patent application Ser. No. 11/388,919 filed Mar. 24, 2006 entitled PRESSURE REGULATION IN AN AUTOMATIC TRANSMISSION). Algorithms exist for pressure sensor correction with respect to temperature. Such algorithms correct pressure sensor drift or offset over time due to sensor variation and degradation. The closed loop pressure system relies on accurate pressure sensing information to provide the improved accuracy desired.